JPH08270691A - Disc brake for two-system type vehicle - Google Patents

Abstract

PURPOSE: To prevent incurring of a hydraulic pressure loss as much as possible and to exert thrust of a small diameter piston on the whole of a friction pad as uniformly as possible by a method wherein a small piston is inserted in the piston insertion hole of a large piston and a gap between the piston insertion hole of a large piston and the small piston is sealed in a liquidtight manner with a sealant. CONSTITUTION: A small piston 29 is arranged in a protruding state through the piston insertion hole 38 of a large piston 28 into the large piston 28, and a gap between the piston insertion hole 38 of the large piston 28 and a small piston 29 in the piston insertion hole 38 is sealed in a liquidtight manner with a sealant 40 having the same inside diameter as that of a small square seal 35 between a small cylinder hole 27 and the small piston 29. Through individual operation of the large piston 28 and the small piston 29 regardless of the other, brake operation is effected. Further, a liquid pressure in a large liquid pressure chamber 31 is effectively exerted only as thrust by which the large piston 28 is advanced in the direction of a disc rotor 22 and a liquid pressure in the small liquid chamber 31 is effectively exerted as thrust by which the small piston 29 is advanced in the direction of the disc rotor 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc brake used in a traveling vehicle such as an automobile or a motorcycle. More specifically, the action portion of a caliper body is provided with two large and small pistons coaxially with each other. The present invention relates to a two-system type vehicle disc brake in which pistons are operated in different hydraulic systems.

[0002]

2. Description of the Related Art A two-system type vehicle disc brake is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-216353. FIG. 5 is an enlarged view of a main part of the above-mentioned conventional example, in which a large-diameter cylinder hole 4 is provided in an action part 3a of a caliper body 3 which is disposed on a side part of a disk rotor 1 with a friction pad 2 interposed therebetween.
And the small diameter cylinder hole 5 are connected on the same axis,
A large-diameter piston 6 having a bottomed cylindrical shape is inserted into the large-diameter cylinder hole 4 through a square seal 7 so as to be liquid-tight and movable, and a bottom wall 6a of the large-diameter piston 6 and a bottom wall of the large-diameter cylinder hole 4 are inserted. A large-diameter hydraulic chamber 8 is defined between the small-diameter cylinder hole 5 and the small-diameter cylinder hole 5b.
A small-diameter piston 9 is liquid-tightly and movably inserted through a square seal 10, and a small-diameter hydraulic chamber 11 is defined between the small-diameter piston 9 and the bottom wall 3c of the small-diameter cylinder hole 5.

The hydraulic chambers 8 and 11 are provided with union holes 12 and 13 communicating with the outer surface of the working portion 3a. Different unillustrated hydraulic systems are connected to the union holes 12 and 13, respectively. The hydraulic fluid, which has been increased in pressure from each hydraulic system, is supplied to the hydraulic chambers 8 and 11 so that the large-diameter piston 6 and the small-diameter piston 9 can be individually pushed in the disk direction. Bottom wall 6a of large-diameter piston 6
The recess 6b is provided in the recess 6b, and the small-diameter piston 9 is provided in the recess 6b.
A head flange 9a of the head flange 9a is protruded and fixed by a circlip 14, and a gap C1 is provided between a distance W1 between the recess 6b and the circlip 14 and a thickness T1 of the head flange 9a.
(Not shown) is set so that the clearance C1 allows the pistons 6 and 9 to operate with a margin.

[0004]

When the braking action is performed from such a configuration, the hydraulic pressure P1 of the hydraulic fluid supplied to the large diameter hydraulic chamber 8 presses the bottom wall 6a of the large diameter piston 6. And acts as a thrust for advancing the large-diameter piston 6 toward the disc rotor, and a part of the large-diameter piston 6 enters between the recess 6b of the large-diameter piston 6 and the head flange 9a of the small-diameter piston 9 to move the small-diameter piston 9 into the disc. Since it acts as a reverse thrust that pushes in the opposite direction to the rotor, it results in a loss of hydraulic pressure P1. In order to further operate the small diameter piston 9 in the disc rotor direction, the hydraulic fluid supplied to the small diameter hydraulic chamber 11 is used. Since it is necessary to increase the pressure P2 to overcome the reverse thrust P1, the hydraulic pressure P2 is also lost, and the total thrust of the hydraulic pressures P1 and P2 with respect to the friction pad 2 is reduced.

When the hydraulic fluid is supplied only to the small-diameter hydraulic chamber 11, the small-diameter piston 9 moves in the disc rotor direction to push the large-diameter piston 6, but the large-diameter hydraulic chamber is used. If the large-diameter piston 6 moves toward the disc rotor without supplying hydraulic fluid to the large-diameter hydraulic pressure chamber 8, the large-diameter hydraulic chamber 8 becomes a negative pressure, and the negative pressure increases as the large-diameter hydraulic chamber 8 expands. The large-diameter piston 6 acts as an operating resistance of the small-diameter piston 9, and the hydraulic pressure P2 is lost.

The present invention has been made in view of the above circumstances, and an object thereof is to minimize the hydraulic pressure loss of the hydraulic fluid while operating the large diameter piston and the small diameter piston independently. Therefore, it is another object of the present invention to provide a disc brake for a two-system type vehicle in which the hydraulic pressure of the hydraulic fluid can be effectively applied to the friction pad as a thrust force and the thrust force of the small diameter piston can be uniformly applied to the entire friction pad as much as possible.

[0007]

According to the above-mentioned object, the first
According to the invention, a large-diameter cylinder hole opening to the disk rotor side and a small-diameter cylinder opening to the bottom wall of the large-diameter cylinder hole are provided in the action part of the caliper body which is disposed on the side part of the disk rotor with the friction pad interposed therebetween. Connect the hole and the same axis,
A large-diameter piston is liquid-tightly and movably inserted into the large-diameter cylinder hole via a large-diameter angle seal, and a large-diameter hydraulic chamber is provided between the large-diameter piston and the bottom wall of the large-diameter cylinder hole. A small-diameter piston is liquid-tightly and movably inserted into the small-diameter cylinder hole through a small-diameter square seal, and a small-diameter hydraulic chamber is defined between the small-diameter piston and the bottom wall of the small-diameter cylinder hole. Then, different hydraulic systems are respectively connected to the small diameter hydraulic chamber and the large diameter hydraulic chamber, and to the pressurized hydraulic fluid supplied from each hydraulic system to the large diameter hydraulic chamber or the small diameter hydraulic chamber. In the two-system type vehicle disc brake for individually braking the large-diameter piston and the small-diameter piston in the disc direction, a piston insertion hole is formed through the large-diameter piston in the axial direction. Extend the small diameter piston to the large diameter piston side The small-diameter piston is inserted into the piston insertion hole of the large-diameter piston so that the tip end surface of the small-diameter piston faces the back surface of the friction pad, and the piston insertion hole of the large-diameter piston and the small-diameter piston in the piston insertion hole are formed. The space between them is liquid-tightly sealed with a sealing material having the same inner diameter as the small-diameter square seal.

According to a second aspect of the present invention, in the first aspect of the invention described above, the large-diameter piston is formed in a cylindrical shape with a bottom, and the large-diameter piston is provided in the large-diameter cylinder hole with its bottom wall facing the large-diameter hydraulic chamber side. By inserting, the tip side of the small diameter piston is expanded in the inside of the large diameter piston to form the expanded diameter tip portion, and between the step portion of the expanded diameter tip portion and the bottom wall of the large diameter piston, the braking clearance is A long gap is set, and the gap is communicated with the atmosphere through the enlarged diameter tip of the small diameter piston and the large diameter piston.

As components of the braking clearance BC of the second invention, there are a clearance C2 between the tip of the large-diameter piston and the back surface of the friction pad and a clearance C3 between the friction pad and the disk rotor, and when the caliper body is a pin slide type. Is the braking clearance BC of the second aspect of the invention because the caliper body slides toward the action part by the piston that pushes the friction pad on the action part side, and the friction pad on the reaction part side is also pushed. Of the reaction part and the reaction part = 2 × (C2 + C3), and when the caliper body is a piston facing type, the piston of each operation part pushes only the respective friction pad,
The braking clearance BC of the second invention = clearance of one acting portion of the caliper body = C2 + C3.

[0010]

[Function] By sealing the space between the piston insertion hole of the large-diameter piston and the small-diameter piston with a seal material having the same inner diameter as the small-diameter square seal, the hydraulic pressure supplied to the large-diameter hydraulic chamber is small. The small-diameter piston between the seal and the seal member acts only around the axis, but does not act in the axial direction of the small-diameter piston. Therefore, the hydraulic pressures of the large-diameter hydraulic chamber and the small-diameter hydraulic chamber act only as thrust forces for individually operating the large-diameter piston and the small-diameter piston in the disk rotor direction.

According to the second aspect of the present invention, by forming the enlarged diameter tip portion in which the piston diameter is expanded on the tip side of the small diameter piston, the pad pressing area of the small diameter piston against the friction pad is expanded, and the pad pressing force per unit area is increased. That is, the surface pressure becomes small and the pressing force of the friction pad is dispersed over a wide area of the friction pad, so that the thrust force from the small diameter piston can be applied to the friction pad as evenly as possible.

In the second aspect of the invention, when a gap longer than the braking clearance is set between the step portion of the enlarged diameter tip and the bottom wall of the large diameter piston, both pistons operate independently. It does not interfere with the other, and by communicating this gap with the atmosphere, even if the gap is expanded or contracted by the operation of the piston, the pressure within the interval does not increase or decrease, and therefore the operation of the piston is not hindered.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. Incidentally, in the description of the embodiments, reference numerals are attached to names not shown in order to facilitate understanding, but in order to distinguish from the reference numerals in the figure, the reference numerals of the names not shown are enclosed in {} and displayed.

The caliper body 21 used for the disc brake 20 is supported by a caliper bracket 23 fixed to the vehicle body at one side of the disc rotor 22 so as to be slidable in the disc axial direction by using a slide pin (not shown). Pin slide type, action part 2 of caliper body 21
A pair of friction pads 2 is provided between the lathe 1a and the reaction portion 21b.
4, 25 are arranged to face each other with the disc rotor 22 interposed therebetween.

The caliper body 21 is composed of the above-mentioned action portion 21a and reaction portion 21b which are opposed to the disc rotor 22 with the friction pads 24 and 25 interposed therebetween, and the bridge portion 21c which connects them to each other across the outer periphery of the disc rotor 22. Has become. Two large and small cylinder holes 26 and 27 are continuously provided in the action portion 21a, and the reaction force claw 21 is provided in the reaction portion 21b.
d is extended to the back surface of the back plate 25a of the friction pad 25.

The large diameter cylinder hole 26 is provided so as to open to the back surface of the back plate 24a of the action portion side friction pad 24, and the small diameter cylinder hole 27 is located on the same axis as the large diameter cylinder hole 26. The bottom wall 21e of 26 is provided with an opening. The large diameter cylinder hole 26 and the small diameter cylinder hole 27 have a bottomed cylindrical large diameter piston 28 and a small diameter piston 29, respectively.
However, each of the bottom walls 28a and 29a has a cylinder hole 26,
27 is inserted into the bottom walls 21e and 21f of the large-diameter cylinder 27, and a large-diameter hydraulic chamber 30 is defined between the large-diameter piston 28 and the bottom wall 21e of the large-diameter cylinder hole 26. Between the bottom wall 21f of the cylinder hole 27 and the small diameter hydraulic chamber 3
1 is defined.

Large diameter cylinder hole 26 and small diameter cylinder hole 27
The large-diameter square seal 3
4 and the small-diameter angle seal 35 are fitted to each other, and the angle seal 34,
The large-diameter hydraulic chamber 30 and the small-diameter hydraulic chamber 31 are liquid-tightly sealed at 35, and the large-diameter piston 28 is movably held by the large-diameter square seal 34 in the large-diameter cylinder hole 26. A small-diameter piston 29 is movably held by a small-diameter angle seal 35 in the small-diameter cylinder hole 27. In addition, the pistons 28 and 29 during braking use the corner seals 34 and 3 respectively.
While elastically deforming 5, the cylinder holes 26 and 27 are moved toward the disc rotor, and after the braking operation is released, the corner seal 3
The pistons 28, 29 are pulled back to the predetermined retracted limit positions of the cylinder holes 26, 27 by the restoring force of 4, 35.

The hydraulic chambers 30 and 31 are provided with union holes 36 and 37 communicating with the outer surface of the working portion 21a. The union holes 36 and 37 are connected to different hydraulic systems (not shown). In this manner, the hydraulic fluid whose pressure is increased from each hydraulic system is supplied to the hydraulic chambers 30 and 31, and the large diameter piston 28 and the small diameter piston 29 can be individually or integrally moved in the disk direction. .

A piston insertion hole 38 having the same diameter as that of the small diameter piston 29 is formed through the bottom wall 28a of the large diameter piston 28, and a seal groove 39 is provided around the piston insertion hole 38. A seal member 40 having the same inner diameter as that of the small-diameter square seal 35 is fitted into the piston insertion hole 38, and a small-diameter piston 29 is liquid-tightly inserted into the piston insertion hole 38 via the seal member 40. In the sealing material 40, since the restoring force of the small diameter piston 29 is set in the small diameter piston 29,
An O-ring or the like having only the sealing function may be used, but a square seal may be applied to the sealing material 40 to share the restoring force with respect to the small diameter piston 29.

The small-diameter piston 29 penetrates from the small-diameter cylinder hole 27 through the large-diameter hydraulic chamber 30 and the piston insertion hole 38 of the large-diameter piston 28, projects into the large-diameter piston 28, and has an opening surface at the tip. Is disposed so as to face the rear surface of the back plate 24a of the action portion side friction pad 24 from the inside of the opening surface of the large-diameter piston 28, and the entire length from the end surface of the bottom wall 29a to the opening surface at the tip is the same diameter. Has been formed.

The present embodiment is constructed as described above, and on the working portion 21a side, the small-diameter piston 29 is inserted into the piston insertion hole 38 of the large-diameter piston 28, and the opening surface at the tip is located on the working portion side. By facing the back surface of the back plate 24a of the friction pad 24, the pistons 28 and 29 are moved from their respective hydraulic systems to the hydraulic chamber 3 through the union holes 36 and 37.
The hydraulic fluid supplied to 0 and 31 enables the discs to operate individually or simultaneously in the disk direction.
As a result, at the time of braking, the large-diameter piston 28 and the small-diameter piston 29 push the friction pad 24 individually or simultaneously on the side of the action portion 21a, so that the lining 24 of the friction pad 24 is moved.
b on one side of the disc rotor 22, and on the reaction portion 21b side, the reaction force claw 21d of the caliper body 21 that slides toward the action portion by the braking reaction force pushes the friction pad 25 on the reaction portion side. , Lining 2 of friction pad 25
5b is pressed to the other side surface of the disc rotor 22 to perform a braking action.

The small-diameter piston 29 has a large-diameter hydraulic chamber 30.
Is sealed liquid-tight by the small-diameter angle seal 35 of the small-diameter cylinder hole 27 and the sealing material 40 of the bottom wall 28a of the large-diameter piston 28, and the small-diameter angle seal 35 and the sealing material 40 have the same inner diameter. As a result, small-diameter square seal 3
The outer diameter of the small-diameter piston 29 between the seal 5 and the seal member 40 has the same diameter without a step, so the hydraulic pressure of the hydraulic fluid supplied to the large-diameter hydraulic chamber 30 is the small-diameter angle seal 35 of the small-diameter piston 29.
Although it acts between the seal member 40 and the seal member 40 in the radial direction, it does not act on the small-diameter piston 29 as thrust in the disc rotor direction or reverse thrust in the anti-disc rotor direction. Therefore, when each hydraulic system is operated individually, the large diameter hydraulic chamber 30
The hydraulic pressure inside acts on the large-diameter piston 28, and the hydraulic pressure inside the small-diameter hydraulic chamber 31 acts effectively only as thrust for advancing the small-diameter piston 29 in the direction of the disc rotor, and the opposite thrust acts on the other piston. Similarly, since the other hydraulic chamber is not made negative, there is almost no loss of hydraulic pressure, and the braking force set in each hydraulic system can be effectively exerted.

The small-diameter piston 29 in the large-diameter hydraulic chamber 30
By forming projections and depressions such as embossing and a flange on the outer peripheral surface of the piston, both pistons 28 and 29 before being attached to the caliper body 21 are temporarily assembled in advance and integrated into the cylinder holes 26 and 27. You can also wear it. In this case, the unevenness such as embossing or the flange receives the hydraulic pressure in the large diameter hydraulic chamber 30, but unlike the step only on one side when the small diameter piston 29 is a stepped shaft having a different shaft diameter,
Since the disk rotor side surface and the counter disk rotor side surface are formed on the unevenness and the flange, and the hydraulic pressure applied to both side surfaces is canceled, the hydraulic pressure in the large diameter hydraulic chamber 30 is applied to the small diameter piston 29 to the disk shaft. Does not act as thrust force or reverse thrust force.

3 and 4 show another embodiment of the present invention, in which the small-diameter piston 29 penetrates from the end face of the bottom wall 29a to the piston insertion hole 38 of the large-diameter piston 28, and then the large-diameter piston 28. Is formed coaxially up to the portion projecting inward, and the tip end side is expanded to the same diameter as the inner diameter of the large-diameter piston 28, and this expanded diameter portion is used as the expanded diameter tip portion 29b,
The front end opening surface of the enlarged diameter tip portion 29b faces the back surface of the back plate 24a of the action portion side friction pad 24 from the inside of the large diameter piston 28.

There are flat chamfers at a plurality of points on the outer peripheral surface of the enlarged diameter tip portion 29b, and when the enlarged diameter tip portion 29b is inserted into the large diameter piston 28, it is expanded with the inner periphery of the large diameter piston 28. An atmosphere communication hole 41 is defined between the chamfer of the diameter tip portion 29b and the air communication hole 41. Further, a gap C4, which is longer than a braking clearance {BC} described later, is set between the step portion of the diameter-expanded tip portion 29b and the bottom wall 28a of the large-diameter piston 28, and the gap C4 is the atmosphere communication hole described above. Caliper body 2 through 41
It communicates with the outside of 1.

The components of the braking clearance {BC} include the clearance {C2} between the tip of the large diameter piston and the back surface of the friction pad and the clearance {C3} between the friction pad and the disc rotor. When the caliper body 21 is a pin slide type, the caliper body 21 slides by the operation of the pistons 28 and 29 that push the friction pad 24 on the action portion 21a side, and the reaction force claw 21
Since d pushes the friction pad 25 on the reaction portion 21b side, the braking clearance {BC} of this embodiment = both clearances on the action portion 21a side and the reaction portion 21b side of the caliper body 21 = {2x (C2 + C3) } Becomes.

In the present embodiment, the small diameter piston 29 has an enlarged diameter tip portion 29b formed by expanding the diameter of the piston, so that the pad pressing area of the small diameter piston 29 against the friction pad 24 on the working portion side is expanded. Since the pad pressing force per unit area, that is, the surface pressure is reduced and the friction pad pressing force is dispersed over a wide area of the friction pad 24, the thrust from the small diameter piston 29 can be applied to the friction pad 24 as evenly as possible. Like Also, the expanded diameter tip 29
By setting a gap C4 longer than the braking clearance {BC} between the stepped portion of b and the bottom wall 28a of the large-diameter piston 28, when both pistons 28 and 29 operate independently, they interfere with each other. And the gap C4
Is communicated with the outside of the caliper body 21 through the atmosphere communication hole 41, so that when the pistons 28 and 29 individually operate, they do not interfere with the other piston, and the gaps are generated by the operation of the pistons 28 and 29. Even if C4 expands or contracts, the pressure in the interval C4 does not increase or decrease, so that the operation of the pistons 28, 29 is not hindered.

In the first aspect of the invention, the large-diameter piston and the small-diameter cylinder hole may have any shape of a bottomed cylinder and a columnar body of Muku, and at least the large-diameter piston of the second invention has a bottomed cylindrical shape. It may be formed in. The present invention can also be applied to a disc brake in which the caliper body is a piston facing type.

[0029]

According to the present invention, a piston insertion hole is formed through a bottom wall of a large-diameter piston inserted in a large-diameter hydraulic cylinder toward a large-diameter hydraulic chamber, and a small diameter inserted in a small-diameter cylinder hole. The piston is extended to the large-diameter piston side, and the small-diameter piston is arranged so as to project from the piston insertion hole of the large-diameter piston to the inside of the large-diameter piston, and the piston insertion hole of the large-diameter piston and the small-diameter piston in the piston insertion hole are The space between the small-diameter cylinder hole and the small-diameter piston is liquid-tightly sealed with a small-diameter angle seal and a seal material with the same inner diameter, so that the large-diameter piston and the small-diameter piston operate individually regardless of the other, and braking action is achieved. You will be able to do it. Further, the hydraulic pressure of the hydraulic fluid supplied to the large-diameter hydraulic chamber does not act on the small-diameter piston as thrust in the disc rotor direction or reverse thrust in the anti-disc rotor direction. The hydraulic pressure in the large-diameter piston and the hydraulic pressure in the small-diameter hydraulic chamber effectively act only as thrust for advancing the small-diameter piston in the direction of the disk rotor, and the opposite thrust is applied to the other piston.
Similarly, since the other hydraulic chamber is not made negative, there is almost no loss of hydraulic pressure, and the braking force set in each hydraulic system can be effectively exerted.

Further, the tip side of the small-diameter piston is expanded inside the large-diameter piston to form an expanded-diameter tip portion, and a braking is applied between the step portion of the expanded-diameter tip portion and the bottom wall of the large-diameter piston. By setting a gap that is longer than the clearance and communicating the gap with the atmosphere through the expanded tip of the small diameter piston and the large diameter piston, the pad pressing area of the small diameter piston against the friction pad is expanded to a unit area. The pad pressing force per contact, that is, the surface pressure is reduced, and the friction pad pressing force is dispersed over a wide area of the friction pad, so that the thrust from the small diameter piston can be applied to the friction pad as evenly as possible. In addition, the large diameter piston and the small diameter piston
Even if they operate independently, they do not interfere with each other, and even if the gap between the stepped portion of the diameter expansion tip and the bottom wall of the large diameter piston is expanded or contracted by the operation of these pistons, Since air can be sucked and discharged, it does not hinder the operation of the piston.

[Brief description of drawings]

FIG. 1 is a sectional front view of a disc brake showing an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a large-diameter piston, a small-diameter piston, and a sealing material of a disc brake showing an embodiment of the present invention.

FIG. 3 is a sectional front view of a disc brake showing another embodiment of the present invention.

FIG. 4 is an exploded perspective view of a large-diameter piston, a small-diameter piston, and a sealing material of a disc brake according to another embodiment of the present invention.

FIG. 5 is an enlarged view of a main part of a conventional disc brake.

[Explanation of symbols]

Reference numeral 20 ... Disc brake 21 ... Pin slide type caliper body 22 ... Disc rotor 24 ... Friction pad on working portion 21a side 25 ... Friction pad on reaction portion 21b side 21a ... Working portion 21b of caliper body 21 ... Reaction portion of caliper body 21 21c ... Bridge part of caliper body 21e ... Bottom wall of large diameter cylinder hole 26 21f ... Bottom wall of small diameter cylinder hole 27 ... Large diameter cylinder hole 27 ... Small diameter cylinder hole 28 ... Large diameter piston 28a ... Large diameter piston 28 Bottom wall 29 ... Small-diameter piston 29a ... Bottom wall 29b of small-diameter piston 29 ... Expanded diameter end 30 ... Large-diameter hydraulic chamber 31 ... Small-diameter hydraulic chamber 32, 33 ... Seal groove 34 ... Large-diameter angle seal 35 ... Small-diameter angle seal 36, 37 ... Union hole 38 ... Piston insertion hole 39 ... Seal groove 40 ... Sealing material such as O-ring 41 ... Large Gap between the bottom wall 28a of the communication hole C4 ... enlarged distal portion 29b of the stepped portion and the large diameter piston 28

Claims (2)

[Claims] Claim: What is claimed is: 1. A large-diameter cylinder hole opening to the disk rotor side, and a large-diameter cylinder hole opening to the bottom wall of the large-diameter cylinder hole. A small-diameter cylinder hole is continuously provided on the same axis, and a large-diameter piston is liquid-tightly and movably inserted into the large-diameter cylinder hole through a large-diameter angle seal. A large-diameter hydraulic chamber is defined between the small-diameter piston and the small-diameter cylinder hole, and a small-diameter piston is inserted into the small-diameter cylinder hole via a small-diameter square seal so as to be liquid-tight and movable. A small-diameter hydraulic chamber is defined between the bottom wall and different hydraulic systems are connected to the small-diameter hydraulic chamber and the large-diameter hydraulic chamber, and the large-diameter hydraulic chamber or the large-diameter hydraulic chamber is connected from each hydraulic system. With the pressurized hydraulic fluid supplied to the small diameter hydraulic chamber, In a two-system vehicle disc brake that individually pushes pistons in the disc direction to perform braking action, a piston insertion hole is formed through the large-diameter piston in the axial direction, and the small-diameter piston is attached to the large-diameter piston side. The small-diameter piston is inserted into the piston insertion hole of the large-diameter piston so that the tip end surface of the small-diameter piston faces the back surface of the friction pad, and the piston insertion hole of the large-diameter piston and the piston insertion hole are formed. A disc brake for a two-system type vehicle, wherein a space between a small-diameter piston therein and a small-diameter square seal is liquid-tightly sealed by a seal material having the same inner diameter. 2. The large-diameter piston is formed in a cylindrical shape with a bottom, and the large-diameter piston is inserted into a large-diameter cylinder hole with a bottom wall facing the large-diameter hydraulic chamber side, and a tip side of the small-diameter piston. Is enlarged inside the large-diameter piston as a diameter-expanding tip, and a gap longer than the braking clearance is set between the step portion of the diameter-expanding tip and the bottom wall of the large-diameter piston. 2. The disc brake for a two-system vehicle according to claim 1, wherein the gap is made to communicate with the atmosphere through a gap between the enlarged diameter tip of the small diameter piston and the large diameter piston.